Patent Literature 1 describes a light deflector that includes an oscillating body including a mirror and a torsion spring for rotatably supporting the mirror, a fixing unit to which the oscillating body is fixed, and a driving unit configured to reciprocally vibrate the mirror by deforming the torsion spring with its resonance frequency.
The mirror includes a base made of silicon. A refection film made of metal U (Al or Au) is formed on the base.
In the aforementioned light deflector, the temperature of the reflection film rises due to absorption of a part of incident light on the reflection film. As a result, distortion occurs in the mirror (especially, in the base) because of thermal expansion. When the distortion occurs in the mirror, accurate scanning with the optical beam is difficult.
The temperature increase causes a change in rigidity of the torsion spring, thereby changing the resonance frequency of the torsion spring. The change of the resonance frequency of the torsion spring is accompanied by the change of a deflection angle. As a result, accurate scanning with the optical beam is difficult.
Thus, Patent literature 1 describes a light deflector that has a heat releasing structure. This light deflector includes, in addition to the oscillating body, the fixing unit, and the driving unit described above, a solid heat transfer body that covers the oscillating body. The solid heat transfer body is made of metal such as Al. Heat generated by light absorption is released from the reflection film through the solid heat transfer body to the outside.
Further, Patent Literature 2 describes an image display device that includes a light source, a MEMS mirror configured to scan a screen with an optical beam from the light source, an auxiliary light source configured to irradiate the MEMS mirror with an optical beam, and control means for controlling power of the auxiliary light source to keep the temperature of the MEMS mirror constant.
The MEMS mirror includes a mirror unit including a dielectric multilayer film, a first substrate on which the mirror unit is mounted, two beams for rotatably supporting the first substrate, and a second substrate to which the beams are fixed. The beams and the second substrate correspond to the aforementioned torsion spring.
In the MEMS mirror, a part of incident light from the light source is reflected on the dielectric multilayer film, and the remainder of the light is absorbed by the dielectric multilayer film or the first substrate. Reflectance of the dielectric multilayer film in the wavelength region of the light from the light source is 98% or higher.
The light from the auxiliary light source is also applied to the mirror unit of the MEMS mirror. The wavelength region of the auxiliary light source is different from that of the light source. Reflectance of the dielectric multilayer film in the wavelength region of the auxiliary light source is several %. Accordingly, most of the light from the auxiliary light source is absorbed by the dielectric multilayer film or the first substrate.
In the image display device, the control means controls the amount of light emitted from the auxiliary light source so that the sum total of the energy amount of the light emitted from the light source and absorbed by the mirror unit and the energy amount of the light emitted from the auxiliary light source and absorbed by the mirror unit can be constant.